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  • 1
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    Quantifying subtropical North Pacific gyre mixed layer primary productivity from Seaglider observations of diel oxygen cycles (2015)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: © The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Geophysical Research Letters 42 (2015): 4032–4039, doi:10.1002/2015GL063065.
    Description: Using autonomous underwater gliders, we quantified diurnal periodicity in dissolved oxygen, chlorophyll, and temperature in the subtropical North Pacific near the Hawaii Ocean Time-series (HOT) Station ALOHA during summer 2012. Oxygen optodes provided sufficient stability and precision to quantify diel cycles of average amplitude of 0.6 µmol kg−1. A theoretical diel curve was fit to daily observations to infer an average mixed layer gross primary productivity (GPP) of 1.8 mmol O2 m−3 d−1. Cumulative net community production (NCP) over 110 days was 500 mmol O2 m−2 for the mixed layer, which averaged 57 m in depth. Both GPP and NCP estimates indicated a significant period of below-average productivity at Station ALOHA in 2012, an observation confirmed by 14C productivity incubations and O2/Ar ratios. Given our success in an oligotrophic gyre where biological signals are small, our diel GPP approach holds promise for remote characterization of productivity across the spectrum of marine environments.
    Description: The authors acknowledge support from the National Science Foundation (NSF) through an NSF Science and Technology Center, the Center for Microbial Oceanography Research and Education (C-MORE; NSF EF-0424599). D.N. also was supported by NSF (OCE-1129644) and an Independent Study Award from the Woods Hole Oceanographic Institution (WHOI). D.M.K. was also supported by the Gordon and Betty Moore Foundation. WHOI Summer Student Fellow Cole Stites-Clayton, Stanford University, contributed to early stages of Seaglider data analysis and was supported by an NSF REU grant to WHOI (OCE-1156952).
    Keywords: Primary productivity ; Glider ; Diel ; Oxygen ; Net community production ; Hawaii
    Repository Name: Woods Hole Open Access Server
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  • 2
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    Estimating hypoxic volume in the Chesapeake Bay using two continuously sampled oxygen profiles (2018)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: © The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Journal of Geophysical Research: Oceans 123 (2018): 6392-6407, doi:10.1029/2018JC014129.
    Description: Low levels of dissolved oxygen (DO) occur in many embayments throughout the world and have numerous detrimental effects on biota. Although measurement of in situ DO is straightforward with modern instrumentation, quantifying the volume of water in a given embayment that is hypoxic (hypoxic volume (HV)) is a more difficult task; however, this information is critical for determining whether management efforts to increase DO are having an overall impact. This paper uses output from a three‐dimensional numerical model to demonstrate that HV in Chesapeake Bay can be estimated well with as few as two vertical profiles. In addition, the cumulative hypoxic volume (HVC; the total amount of hypoxia in a given year) can be calculated with relatively low uncertainty (〈10%) if continuous DO data are available from two strategically positioned vertical profiles. This is because HV in the Chesapeake Bay is strongly constrained by the geometry of the embayment. A simple Geometric HV calculation method is presented and numerical model results are used to illustrate that for calculating HVC, the results using two daily‐averaged profiles are typically more accurate than those of the standard method that interpolates bimonthly cruise data. Bimonthly data produce less accurate estimates of HVC because high‐frequency changes in oxygen concentration, for example, due to regional‐weather‐ or storm‐induced changes in wind direction and magnitude, are not resolved. The advantages of supplementing cruise‐based sampling with continuous vertical profiles to estimate HVC should be applicable to other systems where hypoxic water is constrained to a specific area by bathymetry.
    Description: NOAA Grant Number: NA13NOS0120139
    Keywords: Chesapeake Bay ; Oxygen ; Dead zone ; Hypoxia ; Observing systems ; Estuary
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  • 3
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    Impact of seabed resuspension on oxygen and nitrogen dynamics in the northern Gulf of Mexico : a numerical modeling study (2018)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: © The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Journal of Geophysical Research: Oceans 123 (2018): 7237-7263, doi:10.1029/2018JC013950.
    Description: Resuspension affects water quality in coastal environments by entraining seabed organic matter into the water column, which can increase remineralization, alter seabed fluxes, decrease water clarity, and affect oxygen and nutrient dynamics. Nearly all numerical models of water column biogeochemistry, however, simplify seabed and bottom boundary layer processes and neglect resuspension. Here we implemented HydroBioSed, a coupled hydrodynamic‐sediment transport‐biogeochemical model to examine the role of resuspension in regulating oxygen and nitrogen dynamics on timescales of a day to a month. The model was implemented for the northern Gulf of Mexico, where the extent of summertime hypoxia is sensitive to seabed and bottom boundary layer processes. Results indicated that particulate organic matter remineralization in the bottom water column increased by an order of magnitude during resuspension events. This increased sediment oxygen consumption and ammonium production, which were defined as the sum of seabed fluxes of oxygen and ammonium, plus oxygen consumption and ammonium production in the water column due to resuspended organic matter. The increases in remineralization impacted biogeochemical dynamics to a greater extent than resuspension‐induced seabed fluxes and oxidation of reduced chemical species. The effect of resuspension on bottom water biogeochemistry increased with particulate organic matter availability, which was modulated by sediment transport patterns. Overall, when averaged over the shelf and on timescales of a month in the numerical model, cycles of erosion and deposition accounted for about two thirds of sediment oxygen consumption and almost all of the sediment ammonium production.
    Description: DOC | National Oceanic and Atmospheric Administration (NOAA); U.S. National Oceanic and Atmospheric Administration's National Centers for Coastal Ocean Science Center for Sponsored Coastal Ocean Research Grant Numbers: NA09NOS4780231, NA09NOS4780229
    Keywords: Regional Ocean Modeling System (ROMS) ; Northern Gulf of Mexico continental shelf hypoxia ; Sediment transport and resuspension ; Particulate organic carbon (POC) ; Nitrogen ; Oxygen
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  • 4
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    Seasonal and interannual oxygen variability on the Washington and Oregon continental shelves (2015)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2015. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 120 (2015): 608–633, doi:10.1002/2014JC010254.
    Description: The coastal waters of the northern portion of the California Current System experience a seasonal decline in oxygen concentrations and hypoxia over the summer upwelling season that results in negative impacts on habitat for many organisms. Using a regional model extending from 43°N to 50°N, with an oxygen component developed in this study, drivers of seasonal and regional oxygen variability are identified. The model includes two pools of detritus, which was an essential addition in order to achieve good agreement with the observations. The model was validated using an extensive array of hydrographic and moored observations. The model captures the observed seasonal decline as well as spatial trends in bottom oxygen. Spatially, three regions of high respiration are identified as locations where hypoxia develops each modeled year. Two of the regions are previously identified recirculation regions. The third region is off of the Washington coast. Sediment oxygen demand causes the region on the Washington coast to be susceptible to hypoxia and is correlated to the broad area of shallow shelf (〈60 m) in the region. Respiration and circulation-driven divergence contribute similar (60, 40%, respectively) amounts to the integrated oxygen budget on the Washington coast while respiration dominates the Oregon coast. Divergence, or circulation, contributes to the oxygen dynamics on the shelf in two ways: first, through the generation of retention features, and second, by determining variability.
    Description: This work was supported by a postdoctoral fellowship to Samantha Siedlecki from JISAO and the Program on Climate Change at the University of Washington, and grants from the Coastal Ocean Program of the National Oceanic and Atmospheric Administration (NOAA) (NA09NOS4780180) and the National Science Foundation (NSF) (OCE0942675) as part of the Pacific Northwest Toxins (PNWTOX) project.
    Description: 2015-08-05
    Keywords: Hypoxia ; Oxygen ; Respiration ; Upwelling
    Repository Name: Woods Hole Open Access Server
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  • 5
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    Biological production, export efficiency, and phytoplankton communities across 8000 km of the South Atlantic (2017)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2017. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 31 (2017): 1066–1088, doi:10.1002/2016GB005488.
    Description: In situ oxygen tracers (triple oxygen isotope and oxygen/argon ratios) were used to evaluate meridional trends in surface biological production and export efficiency across ~8000 km of the tropical and subtropical South Atlantic in March–May 2013. We used observations of picophytoplankton, nanophytoplankton, and microphytoplankton to evaluate community structure and diversity and assessed the relationships of these characteristics with production, export efficiency, and particulate organic carbon (POC) fluxes. Rates of productivity were relatively uniform along most of the transect with net community production (NCP) between 0 and 10 mmol O2 m−2 d−1, gross primary production (GPP) between 40 and 100 mmol O2 m−2 d−1, and NCP/GPP, a measure of export efficiency, ranging from 0.1 to 0.2 (0.05–0.1 in carbon units). However, notable exceptions to this basin-scale homogeneity included two locations with highly enhanced NCP and export efficiency compared to surrounding regions. Export of POC and particulate nitrogen, derived from sediment traps, correlated with GPP across the transect, over which the surface community was dominated numerically by picophytoplankton. NCP, however, did not correlate with POC flux; the mean difference between NCP and POC flux was similar to published estimates of dissolved organic carbon export from the surface ocean. The interrelated rates of production presented in this work contribute to the understanding, building on the framework of better-studied ocean basins, of how carbon is biologically transported between the atmosphere and the deep ocean.
    Description: National Science Foundation (NSF) Grant Number: OCE 1029676; Gordon and Betty Moore Foundation Grant Grant Number: 537.01; Woods Hole Oceanographic Institution (WHOI); WHOI Devonshire Postdoctoral Scholarship; National Defense Science and Engineering Graduate Fellowship; WHOI Ocean Life Institute; Woods Hole Oceanographic Institution (WHOI) Ocean and Climate Change Institute NSF Grant Numbers: OCE 1029676, OCE 1154320
    Description: 2018-01-11
    Keywords: Oxygen ; Net community production ; Gross primary production ; Carbon flux ; Triple oxygen isotopes ; Argon
    Repository Name: Woods Hole Open Access Server
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  • 6
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    Evaluation of the Southern Ocean O2/Ar-based NCP estimates in a model framework (2013)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Biogeosciences 118 (2013): 385–399, doi:10.1002/jgrg.20032.
    Description: The sea-air biological O2 flux assessed from measurements of surface O2 supersaturation in excess of Ar supersaturation (“O2 bioflux”) is increasingly being used to constrain net community production (NCP) in the upper ocean mixed layer. In making these calculations, one generally assumes that NCP is at steady state, mixed layer depth is constant, and there is no O2 exchange across the base of the mixed layer. The object of this paper is to evaluate the magnitude of errors introduced by violations of these assumptions. Therefore, we examine the differences between the sea-air biological O2 flux and NCP in the Southern Ocean mixed layer as calculated using two ocean biogeochemistry general circulation models. In this approach, NCP is considered a known entity in the prognostic model, whereas O2 bioflux is estimated using the model-predicted O2/Ar ratio to compute the mixed layer biological O2 saturation and the gas transfer velocity to calculate flux. We find that the simulated biological O2 flux gives an accurate picture of the regional-scale patterns and trends in model NCP. However, on local scales, violations of the assumptions behind the O2/Ar method lead to significant, non-uniform differences between model NCP and biological O2 flux. These errors arise from two main sources. First, venting of biological O2 to the atmosphere can be misaligned from NCP in both time and space. Second, vertical fluxes of oxygen across the base of the mixed layer complicate the relationship between NCP and the biological O2 flux. Our calculations show that low values of O2 bioflux correctly register that NCP is also low (〈10 mmol m−2 day−1), but fractional errors are large when rates are this low. Values between 10 and 40 mmol m−2 day−1 in areas with intermediate mixed layer depths of 30 to 50 m have the smallest absolute and relative errors. Areas with O2 bioflux higher than 30 mmol m−2 day−1 and mixed layers deeper than 40 m tend to underestimate NCP by up to 20 mmol m−2 day−1. Excluding time periods when mixed layer biological O2 is undersaturated, O2 bioflux underestimates time-averaged NCP by 5%–15%. If these time periods are included, O2 bioflux underestimates mixed layer NCP by 20%–35% in the Southern Ocean. The higher error estimate is relevant if one wants to estimate seasonal NCP since a significant amount of biological production takes place when mixed layer biological O2 is undersaturated.
    Description: This work was supported in part by funding from the National Aeronautic and Space Administration (NASA NNX08AF12G) and National Science Foundation (NSF OPP-0823101).
    Keywords: Biological production ; Southern Ocean ; O2/Ar ; Modeling ; Oxygen ; GCM
    Repository Name: Woods Hole Open Access Server
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  • 7
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    Using noble gases to compare parameterizations of air‐water gas exchange and to constrain oxygen losses by ebullition in a shallow aquatic environment (2018)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Biogeosciences 123 (2018): 2711-2726, doi:10.1029/2018JG004441.
    Description: Accurate determination of air‐water gas exchange fluxes is critically important for calculating ecosystem metabolism rates from dissolved oxygen in shallow aquatic environments. We present a unique data set of the noble gases neon, argon, krypton, and xenon in a salt marsh pond to demonstrate how the dissolved noble gases can be used to quantify gas transfer processes and evaluate gas exchange parameterizations in shallow, near‐shore environments. These noble gases are sensitive to a variety of physical processes, including bubbling. We thus additionally use this data set to demonstrate how dissolved noble gases can be used to assess the contribution of bubbling from the sediments (ebullition) to gas fluxes. We find that while literature gas exchange parameterizations do well in modeling more soluble gases, ebullition must be accounted for in order to correctly calculate fluxes of the lighter noble gases. In particular, for neon and argon, the ebullition flux is larger than the differences in the diffusive gas exchange flux estimated by four different wind speed‐based parameterizations for gas exchange. We present an application of noble gas derived ebullition rates to improve estimates of oxygen metabolic fluxes in this shallow pond environment. Up to 21% of daily net oxygen production by photosynthesis may be lost from the pond via ebullition during some periods of biologically and physically produced supersaturation. Ebullition could be an important flux of oxygen and other gases that is measurable with noble gases in other shallow aquatic environments.
    Description: NSF. Grant Numbers 1233678, 1238212, DEB 1354494; Woods Hole Oceanographic Institution (WHOI); National Defense Science and Engineering Graduate Fellowship; Northeast Climate Science Center Grant Number: DOI G12AC00001
    Description: 2019-03-07
    Keywords: Bubbles ; Ecosystem metabolism ; Noble gases ; Ebullition ; Oxygen ; Salt marsh pond
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  • 8
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    Plastic formulation is an emerging control of its photochemical fate in the ocean (2021)
    American Chemical Society
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    Publication Date: 2022-10-26
    Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Walsh, A. N., Reddy, C. M., Niles, S. F., McKenna, A. M., Hansel, C. M., & Ward, C. P. Plastic formulation is an emerging control of its photochemical fate in the ocean. Environmental Science & Technology, 55(18), (2021): 12383–12392, https://doi.org/10.1021/acs.est.1c02272.
    Description: Sunlight exposure is a control of long-term plastic fate in the environment that converts plastic into oxygenated products spanning the polymer, dissolved, and gas phases. However, our understanding of how plastic formulation influences the amount and composition of these photoproducts remains incomplete. Here, we characterized the initial formulations and resulting dissolved photoproducts of four single-use consumer polyethylene (PE) bags from major retailers and one pure PE film. Consumer PE bags contained 15–36% inorganic additives, primarily calcium carbonate (13–34%) and titanium dioxide (TiO2; 1–2%). Sunlight exposure consistently increased production of dissolved organic carbon (DOC) relative to leaching in the dark (3- to 80-fold). All consumer PE bags produced more DOC during sunlight exposure than the pure PE (1.2- to 2.0-fold). The DOC leached after sunlight exposure increasingly reflected the 13C and 14C isotopic composition of the plastic. Ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry revealed that sunlight exposure substantially increased the number of DOC formulas detected (1.1- to 50-fold). TiO2-containing bags photochemically degraded into the most compositionally similar DOC, with 68–94% of photoproduced formulas in common with at least one other TiO2-containing bag. Conversely, only 28% of photoproduced formulas from the pure PE were detected in photoproduced DOC from the consumer PE. Overall, these findings suggest that plastic formulation, especially TiO2, plays a determining role in the amount and composition of DOC generated by sunlight. Consequently, studies on pure, unweathered polymers may not accurately represent the fates and impacts of the plastics entering the ocean.
    Description: Funding was provided by the Seaver Institute, the Gerstner Family Foundation, Woods Hole Oceanographic Institution, and the National Science Foundation Graduate Research Fellowship Program (A.N.W.). The Ion Cyclotron Resonance user facility at the National High Magnetic Field Laboratory is supported by the National Science Foundation Division of Chemistry and Division of Materials Research through DMR-1644779 and the State of Florida.
    Keywords: Plastic pollution ; Marine debris ; Additives ; Dissolved organic carbon ; Photochemical oxidation ; FT-ICR-MS ; Titanium dioxide
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  • 9
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    Radiocarbon content of dissolved organic carbon in the South Indian Ocean (2018)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 45 (2018): 872–879, doi:10.1002/2017GL076295.
    Description: We report four profiles of the radiocarbon content of dissolved organic carbon (DOC) spanning the South Indian Ocean (SIO), ranging from the Polar Front (56°S) to the subtropics (29°S). Surface waters held mean DOC Δ14C values of −426 ± 6‰ (~4,400 14C years) at the Polar Front and DOC Δ14C values of −252 ± 22‰ (~2,000 14C years) in the subtropics. At depth, Circumpolar Deep Waters held DOC Δ14C values of −491 ± 13‰ (~5,400 years), while values in Indian Deep Water were more depleted, holding DOC Δ14C values of −503 ± 8‰ (~5,600 14C years). High-salinity North Atlantic Deep Water intruding into the deep SIO had a distinctly less depleted DOC Δ14C value of −481 ± 8‰ (~5,100 14C years). We use multiple linear regression to assess the dynamics of DOC Δ14C values in the deep Indian Ocean, finding that their distribution is characteristic of water masses in that region.
    Description: National Science Foundation (NSF) Grant Numbers: OPP-1142117, OCE-1436748
    Description: 2018-07-24
    Keywords: Radiocarbon ; Dissolved organic carbon ; Indian Ocean
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  • 10
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    The triple oxygen isotope tracer of primary productivity in a dynamic ocean model (2014)
    John Wiley & Sons
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © American Geophysical Union, 2014. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycle 28 (2014): 538–552, doi:10.1002/2013GB004704.
    Description: The triple oxygen isotopic composition of dissolved oxygen (17Δdis) was added to the ocean ecosystem and biogeochemistry component of the Community Earth System Model, version 1.1.1. Model simulations were used to investigate the biological and physical dynamics of 17Δdis and assess its application as a tracer of gross photosynthetic production (gross oxygen production (GOP)) of O2 in the ocean mixed layer. The model reproduced large-scale patterns of 17Δdis found in observational data across diverse biogeographical provinces. Mixed layer model performance was best in the Pacific and had a negative bias in the North Atlantic and a positive bias in the Southern Ocean. Based on model results, the steady state equation commonly used to calculate GOP from tracer values overestimated the globally averaged model GOP by 29%. Vertical entrainment/mixing and the time rate of change of 17Δdis were the two largest sources of bias when applying the steady state method to calculate GOP. Entrainment/mixing resulted in the largest overestimation in midlatitudes and during summer and fall and almost never caused an underestimation of GOP. The tracer time rate of change bias resulted both in underestimation of GOP (e.g., during spring blooms at high latitudes) and overestimation (e.g., during the summer following a bloom). Seasonally, bias was highest in the fall (September-October-November in the Northern Hemisphere, March-April-May in the Southern), overestimating GOP by 62%, globally averaged. Overall, the steady state method was most accurate in equatorial and low-latitude regions where it estimated GOP to within ±10%. Field applicable correction terms are derived for entrainment and mixing that capture 86% of model vertical bias and require only mixed layer depth history and triple oxygen isotope measurements from two depths.
    Description: We acknowledge support from Center for Microbial Oceanography Research and Education (CMORE) (NSF EF-0424599) and NOAA Climate Program Office (NA 100AR4310093).
    Description: 2014-11-23
    Keywords: Primary production ; Triple oxygen isotope ; Photosynthesis ; Gross primary production ; Carbon ; Oxygen
    Repository Name: Woods Hole Open Access Server
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